As a concrete example, it sometimes happens that I'm working on existing code trying to make it faster, because it just isn't up to it's task at the moment. Looking over the code, I can see that it has some code that does a LOT of lookups to see if something is in a collection. And I can see that the collection is using a linked list; which is horrible for lookups. This is something I can notice just browsing through the code because I _already_ know the implementation (and performance) details of a linked list.

At this point, I can take a look at the rest of the code and see if there's some specific reason a linked list was chosen, or if it was just that the developer didn't put much thought into it. If there is a reason (order matters, etc), I can consider what other structures might _also_ suit that need, but also give faster lookups. And, because I know of a variety of data structures, how they're implemented, and what their characteristics are; coming up with some initial choices (or starting points) happens fairly rapidly.

So yes, I could get all this done without knowing all that information. But it happens a LOT faster because I know it. I notice the issue faster. I have some starting points for options faster. Etc.

Not having that information would not prevent me from doing my job. But having that information makes me _better_ at my job. Faster, more efficient, safer, etc.